As an inkjet head, there is a type in which an ink chamber shares an actuator with an ink chamber adjacent to the ink chamber. Such an inkjet head is called a share mode type. In the inkjet head of the share mode type, a plurality of ink chambers partitioned by partition walls made of a piezoelectric material are provided side by side. Electrodes are respectively disposed on the wall surfaces of the ink chambers. Therefore, from an electrical point of view, the inkjet head is equivalent to a series circuit of capacitors.
In such a circuit, stray capacitance is generated between the capacitors connected in series. The stray capacitance is charged or discharged when voltages of the same potential are simultaneously applied to both ends across the capacitors. A noise current is generated in the head according to the charging or the discharging of the stray capacitance. Electric power is uselessly consumed. Such a problem is solved by opening at least one end of the capacitors to a high impedance state.
In the case of the inkjet head of the share mode type, voltages of driving pulses are applied to the electrodes of the ink chambers. Waveforms of the driving pulses are different in a pulse applied to the electrode of the ink chamber communicating with a nozzle that ejects ink and a pulse applied to the electrode of the ink chamber communicating with a nozzle that does not eject ink. However, it could often occur that voltages of the same potential are simultaneously applied to the electrodes of two ink chambers provided side by side across the partition wall.
Therefore, when the voltages of the same potential are simultaneously applied to the electrodes of the two ink chambers, it is conceivable to suppress the noise and the useless power consumption due to the stray capacitance by setting the electrode of one ink chamber to the high impedance state at appropriate timing.
The driving pulses respectively applied to the electrodes disposed in the ink chambers of the inkjet head are generated by a pulse generator (a pattern generator) and output to the inkjet head. Therefore, in order to suppress the noise and the useless power consumption due to the stray capacitance, there is a demand for a generator of driving pulses that can set the electrodes to the high impedance state at appropriate timing.